The present invention relates generally to suspension systems for trucks and trailers and, in a preferred embodiment thereof, more particularly provides a spring beam suspension system.
Suspension systems for large trucks and trailers perform many functions related to the comfort, convenience, and safety of transporting such vehicles on a highway surface. Simply stated, a suspension system acts as an interface between a frame or body of a vehicle and a portion of the vehicle which engages a road surface. The suspension system typically supports or “suspends” the frame and/or body above the road-engaging portion, provides compliance which permits relative motion between them, absorbs shock, adjusts for varied loads and road conditions, structurally interconnects various components of the frame and road-engaging portion, etc.
Many types of suspension systems are well known in the art. One of these is known as a “trailing arm” suspension system. Generally, a trailing arm suspension system incorporates an approximately horizontally disposed arm that is aligned with a direction of travel of a vehicle. A forward end of the arm is usually pivotably attached to a hanger or bracket extending downwardly from the vehicle's frame.
An end of an axle is typically attached to the arm, such that the axle is perpendicular to the arm, and the axle is in most cases rearwardly disposed relative to the hanger. The other end of the axle is likewise attached to another arm. In this manner, the axle is secured to the vehicle and aligned perpendicular to the direction of travel of the vehicle.
A biasing member, such as a spring, is usually connected between the frame and the axle or arm. The spring, thus, biases the frame away from the axle. As a load is added to the vehicle, the spring may compress, or, conversely, as the load is removed from the vehicle, the spring may expand. While the vehicle is being transported across the road surface, the spring may be temporarily compressed as the road-engaging portion strikes an irregularity in the road surface, the spring later expanding when the irregularity has been traversed.
One type of trailing arm suspension system is known as a “spring beam” suspension system. In a spring beam suspension system, the arm is a relatively flexible elongated member known as a “spring beam.” Advantages of a spring beam suspension system include additional vertical compliance afforded by the spring beam and an ability of the spring beam to absorb torsional loads imparted thereto by the axle.
A typical spring beam suspension system is found in U.S. Pat. No. 4,506,910 to Bierens, the entire disclosure of which is incorporated herein by this reference. An axle is rigidly clamped to two transversely spaced apart spring beams. The axle is positioned longitudinally between hangers suspending forward ends of the spring beams from a vehicle frame, and air springs disposed between rear ends of the spring beams and the frame.
If one opposite end of the axle is vertically displaced relative to the other opposite end of the axle, such as when a wheel attached to one end of the axle traverses an irregularity on the road surface, the axle is effectively rotated about a longitudinal axis of the vehicle. Since the axle is rigidly clamped to the spring beam, such rotation is transferred from the axle to the spring beam, causing the spring beam to torsionally flex. Some of this torsional loading is absorbed by a pivot bushing attached to the forward end of the spring beam.
Unfortunately, such spring beam suspension systems do not readily lend themselves to applications in which it is desired to lift the axle (for example, to prevent contact between the wheels and the road surface), the bushing is not always securely retained in the spring beam (which flexes as the axle rotates about the longitudinal axis of the vehicle), and such suspension systems (especially the hanger thereof) are relatively complex and expensive to manufacture and maintain. Therefore, it may be seen that improvements are needed in the art of spring beam suspension systems.